Five New Mars Meteorites Found

FIVE NEW MARS METEORITES FOUND

January 20, 2002
Updated January 22, 2002

Papers on five new Mars meteorites will be presented at the upcoming
33rd Lunar And Planetary Science Conference (LPSC) to be in March 2002 in
Texas. Taking into account pairing, this now raises the number of Mars meteorites
to 24. The new meteorites are:

The two nakhlites are the first to be found in the Antarctic, and at 13.7 kg,
Y000593 is the largest nakhlite ever found. Y000593 is also the second largest
Mars meteorite fragment found, second only to the Zagami meteorite which fell in Nigeria
in 1962. Of additional note, NWA 1068 is the first picritic shergottite because
of its high olivine content. Dhofar 378 unusual in that it is composed predominantly
of maskelynite, a plagioclase glass most likely formed by shock from a large impact event.

Below are excerpts from the abstracts of the papers that will be presented at LPSC.
Note that the total known weight of NWA 1068 is listed as 577 grams in the abstract,
but the finder has informed me that they have found additional fragments which increases
the total weight to 654 grams.

Introduction: North West Africa 1068 (TKM
about 577 g), a new picritic shergottite was found last
April in Moroccan Sahara by meteorite hunters ("La
Memoire de la Terre"). Its synonymous name of
"Louise Michel" (which we have used during the
Met'Soc meeting last september) is preferred to avoid
confusion with the many meteorites of all types reported
under the NWA nomenclature (including now 4
Martian meteorites). In this abstract, its main
petrological and geochemical features will be described.

Petrography: "Louise Michel" is a greenish-
brown rock totally devoid of fusion crust. It displays a
porphyritic texture consisting of a fine-grained
groundmass and olivine grains. Olivines
with various habits occur as clusters often associated
with chromite, or single crystals ranging in size from
50 \265m to 2 millimeters. The largest crystals contain
magmatic inclusions, consisting of two immiscible
silica-rich glasses, Ca-rich pyroxenes and Fe-sulfides.

Chemistry: The bulk composition of "Louise
Michel" has been determined for 45 elements. It is an
Al-poor ferroan basaltic rock, rich in MgO. Its major
element abundances are similar to those reported for
EETA79001A . Key element ratios such as Fe/Mn
(=45), Al/Ti (=6.6), and Ga/Al (=4.4 10-4) are typical
of Martian meteorites. The trace elements demonstrate
unambiguously that "Louise Michel" is unpaired with
any of the other hot desert finds: it is the first picritic
shergottite with a REE pattern similar to those of Shergotty,
Zagami, Los Angeles, and Djel Ibone (NWA 856).

Introduction: 27 meteorites from Mars have been
identified adding of recent findings of 15 meteorites including
paired specimen from hot deserts these five years. Most
of these are classified to be shergottites, and nakhlites have
been limited to be only four including one from a hot desert.
Recent Japanese Antarctic Research Expedition (JARE)
found the heaviest achondrite in Antarctica (Y000593) of
13.7 kg from the bare ice field around the Yamato Mountains.
The petrographical studies and noble gas analyses of the
specimen (Y000593) and paired specimen (Y000749) assured
that these are nakhlites coming from Mars, consisting
with the recent classification. The finding of nakhlites in
Antarctica is for the first time and it suggests that the Yamato
meteorite field potentially includes more unique meteorites.
We describe the analytical results of the meteorite.

Field Occurrence: About 60 % of Y000593 is covered with black
fusion crust, and the interior is greenish colored. Several
days after the finding the quite similar specimen (Y000749 of 1.3 kg)
was found. It is suggested that it is a paired specimen with
Y000593. Two meteorites locate on a bare ice field of the north
of JAREIV nunataks, and the area had insufficiently searched only
by JARE-20. In the area, the heaviest meteorite in the Yamato bare
ice field has been also found by the same expedition of JARE-41.

Conclusion: Our mineralogical-petrographical and
noble gas studies strongly suggest that Y000593 and the
paired specimen Y000749 are a Martian meteorite subclassified into nakhlites.

A meteorite found at Antarctica, which we
have given the tentative name of YA1075,
has been identified as the new martian meteorite
which belong to one of shergottite.
The YA1075 meteorite is 55 grams in
weight which nearly complete stone with
dark green color and partly covered_by the
shiny-black fusion crust. The interior of the
stone shows grey to light grey in color, and
brecciated partly. The stone looks like type
A of the Yamato diogenites especially
Yamato-74013 diogenite for its appearance.
The YA1075 meteorite is also similar to one
of Antarctic martian meteorites such as
ALH-77005 lherzoritic shergottite and
other shergottites.

The YA1075 meteorite consists mostly of
pyroxenes including many olivine grains
poikiliticaly with maskelynized plagioclase
interstitially, and traced some opaques. The
specimen have been identified as one of the
martian meteorite for its mineral assemblages and
mineral compositions, especialy its maskelynized
plagioclase and their compositions(~An50). Clayton
analyzed this meteorite on oxygen isotopic
compositions and he suggested that he
YA1075 meteorite is one of the martian
meteorites based on following oxygen
istopes: 3.95 \245 18O,2.23 \245 17O and
+0.18 \24517O. Oxygen isotope data strongly
supported to authors conclusion.

Plagioclase of the YA1075 meteorite has a very
unique compositons as same as those of the
martian meteorites especially those of shergottites
for example ALH-77005 lherzolitic
shergottites and other shergottites.
However the YA1075 meteorite is quite
differed from those of all known other
achondrites, particularly all of diogenictic
achondrites and all eucrites, and all of the
lunar meteorites. So author concluded that
the YA1075 meteorite is a martian meteorite
belong to one of lherzolitic shergottite.

Introduction: The new shergottite Dhofar 378
was recently recovered from the Oman desert with
fresh black fusion crust. It has a doleritic or micro-gabbroic
texture, and the grain sizes of the main minerals
are about 1 mm in length and a few hundreds of
microns in width. Dhofar 378 is one of the most ferroan
shergottite and may represent a late stage fractional
crystallization product of a Martian magma.

Oxygen isotopes; The oxygen isotopic composition
of the stone was obtained by T.K.Mayeda and
R.N.Clayton. The result is: delta O 18 = +4.46 permil,
and delta O 17 = +2.52 permil, indicating that this stone
is within the range of previously analyzed Martian meteorites.

Pairing; Dhofar 378 was recovered from an
area near the Dhofar 019 basaltic shergottite. Dhofar
019 is doleritic, but it may not be a pair with the new
shergottite. It is because Dhofar 019 contains olivine
grains with Fe/(Mg+Fe) ratios of 0.4-0.75 , although
Dhofar 378 does not contain such magnesian olivine
except for fayalite. Pyroxenes in Dhofar 019 are more
magnesian than those in the new shergottite. Dhofar
378 is rather similar in lithology to Northwest Africa
480, but the latter has a homogeneous maskelynite
(An46-50) and lacks in pyroxferroite.

The GRV9927 meteorite was collected from the
ice sheet in the vicinity of the Grove Hill by
Xiao-Han LIU and Yi-Tai JU from the Academy
Sinica during the 16th Antarctic expedition in 1999.
Based on the observations under polarizing microscope,
scanning electron microscope and electron
probe microanalyses the GRV9927 meteorite is considered
as an ultramafic achondrite. Its mineral and
chemical compositions are quite similar to those of
the ALHA77005 meteorite. It implies that the
GRV9927 meteorite can be recognized as a member
of SNC clan.

The GRV9927 meteorite looks like a rounded
triangular cone. It is 9.97g in weight and partially
covered by dark fusion crust. This meteorite consists
predominantly of olivine and pyroxene. The olivine
crystals have a distinctive brown colour and the pyroxenes
are colourless in thin sections. The structure
and texture are heterogeneous on a centimeter scale.
Both cumulate and poikilitic textures can be seen
under the polarizing microscope. Some euhedral and
pyroxens in certain areas and some euhedral
olivine crystals are enclosed by pyroxenes in other
areas. A small amount of maskelynite, kamacite,
troilite and chromite can be found in the interstices
between olivines and pyroxenes. The mineral composition
of the GRV9927 is intermediate between
pyroxene-rich nakhlites and olivine-rich Chassigny.
In addition, the pyroxene in GRV9927 is mainly orthopyroxene.
It is distinguish from any other SNC
meteorites.

The chemical composition of GRV9927 has been
analyzed using EDS method. The following features
can be recognized in comparison with the SNC meteorites.

1. The major element abundance in GRV9927 is
similar to those in SNC meteorites. The SiO2 contents
in GRV9927 are close to those in shergottites and the
Al2O3 contents are close to those in ALHA77005.
The FeO, MgO, CaO contents are close to
ALHA77005 as well and they are intermediate between
those in nakhlite and Chassigny.

2. Just like other SNC meteorites the high ratio
of Fe/(Fe+Mg) in GRV9927 indicates that it also
formed from differentiated parent magmas.

3. As Ma et al. (1982) reported the compositions
of major and some minor elements among shergotties
have certain colinearities and ALHA77005 and
EETA79001B can be combined in various proportions
to produce the approximate compositions of the
other shergottites [1, 3] . The major element concentrations
in GRV9927 can be projected on this plot. They
just fall into the range and close to the composition of
ALHA77005.